In the cervix there is a nice transition from the rough and tough squamous epithelial cells of the outside world (vagina) to the squishy secretory columnar epithelial cells of the inside (uterus). Over time the junction between these two cell types moves towards the inside (more squamous cells) and this is normal metaplasia. This is not to be confused with dysplasia, which is the transformation of normal squamous cells to less differentiated cells.

When women get colposcopies the examiner is looking for dysplasia, and two of the tricks they have up their sleeves to make the dysplasia more apparent are vinegar and iodine.

Both rely on the fact that dysplastic cells are more active and have a much larger nucleus:cytoplasm ratio.

• When vinegar (acetic acid) is applied, the cells become dehydrated, and the nuclei reflect more light. This makes the cells with larger nuclei more prominent because they appear more white. This includes dysplastic cells and cells infected with HPV.
• With an iodine solution (Lugol’s iodine) the iodine binds to glycogen in cells making them appear dark brown. Healthy columnar cells don’t have glycogen and due to their small amount of cytoplasm, dysplastic and HPV-infected cells don’t either.

Using these two techniques can help differentiate areas of dysplasia and guide sampling biopsies.